Get Reactive With Project Reactor and Spring 5

public interface Subscriber {
public void onSubscribe(Subscription s);
public void onNext(T t);
public void onError(Throwable t);
public void onComplete();
}

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Subscription

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Subscription
public interface Subscription {
public void request(long n);
public void cancel();
}

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Subscription
public interface Subscription {
public void request(long n);
public void cancel();
}

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Subscription

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Processor
Subscription

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Subscription
Processor
public interface Processor
extends Subscriber, Publisher
{}

Example

Project Reactor

by

RxJava-like API

Reactive Types

Flux

like
Stream

Mono

like
CompletableFuture

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Useful Operators

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Operator
==
Very Smart Publisher

merge
.merge(…)

zip
.zip(…)

zip
.zip(…)

publish
.publish(…)

.materialize(…)
materialize

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materialize
.materialize(…)

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Thread A
Thread Main
.publishOn(…)
publishOn

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RxJava.observeOn
==
Reactor.publishOn

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Remember!

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Nothing happens until
.subscribe ()

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Reactivity in Action

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What we`re going to do?

Refactoring

What do we have?

Chat Application

Functionality
• Gitter Chat Communication
• Messaging Statistic

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Demo

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Toolkit
• Spring Framework 4
• Spring Boot
• Spring MVC
• Spring Data JPA

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Architecture

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User Client
Gitter Service
Whole Application
DB Layer
Service Layer
Controllers Layer

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Controllers Layer

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Returns
Thymeleaf View

REST Resources

Services Layer

External Chats SPI

Domain Services

Gitter integration

Implementation

Persistence Layer

Database Model

How it works?

Problems

Problems
• Pulling model

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Problems
• Pulling model
• Too much blocking I/O

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Solutions

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Apply
Reactive Manifesto

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Async Messaging
Push Model

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Apply
Streaming API

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Async Messaging
Elasticity

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Dedicate
ThreadPool

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Async Messaging
Push Model

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Apply WebSocket

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How to bring it all
together?

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Spring 5

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Painless replacement

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WebFlux
@Controller, @RequestMapping,…
Spring MVC
Servlet API
Servlet Container
Spring Web Reactive
Reactive HTTP
Servlet, Netty, Undertow

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@RestController
@RequestMapping("/api/v1/statistics")
public class StatisticResource {
private final StatisticService statisticService;
@Autowired
public StatisticResource(
StatisticService statisticService) {
this.statisticService = statisticService;
}
@GetMapping("/users")
public List getUsersStatistic() {
return statisticService.getUsersStatistic();
}
}

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@RestController
@Autowired
}
public List getUsersStatistic() {
return statisticService.getUsersStatistic();
}
}

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@RestController
@Autowired
}
public Flux getUsersStatistic() {
return Flux.fromIterable(statisticService
.getUsersStatistic());
}

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@RestController
@Autowired
}
public Flux getUsersStatistic() {
return Flux.fromIterable(statisticService
.getUsersStatistic());
}

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Project Reactor + Netty
Integration

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Why Netty?

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Non-Blocking,Reactive
Server

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Reactive Architecture

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Data Base Connection Pipe
Gitter Connection Pipe

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Refactoring Structure

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1. Blocking I/O Refactoring
2. Service Refactoring
3. Endpoints Refactoring
4. Pipeline Testing

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Blocking I/O Refactoring

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Reactive DB Access
via
ReactiveCrudRepository

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interface ReactiveCrudRepository extends Repository
Mono save(S entity);
Flux saveAll(Iterable entities);
Flux saveAll(Publisher entityStream);
Mono findById(ID id);
Mono findById(Mono id);
Mono existsById(ID id);
Mono existsById(Mono id);
Flux findAll();
Flux findAllById(Iterable ids);
Flux findAllById(Publisher idStream);
Mono count();
Mono deleteById(ID id);
Mono delete(T entity);
Mono deleteAll(Iterable extends T> entities);
Mono deleteAll(Publisher extends T> entityStream);
Mono deleteAll();
}

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interface ReactiveCrudRepository extends Repository
Mono save(S entity);
Flux saveAll(Iterable entities);
Flux saveAll(Publisher entityStream);
Mono findById(ID id);
Mono findById(Mono id);
Mono existsById(ID id);
Mono existsById(Mono id);
Flux findAll();
Flux findAllById(Iterable ids);
Flux findAllById(Publisher idStream);
Mono count();
Mono deleteById(ID id);
Mono delete(T entity);
Mono deleteAll(Iterable extends T> entities);
Mono deleteAll(Publisher extends T> entityStream);
Mono deleteAll();
}

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Code session

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.publishOn()
public static Mono mono(
Mono input,
Function<...> transformer
) {
MonoProcessor monoProcessor =
MonoProcessor.create();
input
.publishOn(Schedulers.elastic())
.transform(transformer)
.subscribe(monoProcessor);
return monoProcessor
.subscribeOn(Schedulers.elastic());
}

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.publishOn()
Mono input,
) {
input
}

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.publishOn()
Mono input,
) {
input
}

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.publishOn()
Mono input,
) {
input
}

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.publishOn()
Mono input,
) {
input
}

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.publishOn()
Mono input,
) {
input
}

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Mono input,
) {
input
}
.publishOn()

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Mono input,
) {
input
}
.subscribeOn()
MonoProcessor

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Mono input,
) {
input
}
.subscribeOn()
MonoProcessor

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Mono input,
) {
input
}
MonoProcessor
.subscribeOn()
…subscribe();

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Mono input,
) {
input
}
…subscribe();
MonoProcessor
.subscribeOn()
…subscribe();

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Service Refactoring

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Gitter Service

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Reactive WebClient
out of the box

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public interface WebClient {
UriSpec> get();
//omitted...
static WebClient create() {
return new DefaultWebClientBuilder().build();
}
interface RequestHeadersSpec> {
//omitted...
Mono exchange();
//omitted...
}
interface ResponseSpec {
Mono bodyToMono(Class bodyType);
Flux bodyToFlux(Class elementType);
Mono> toEntity(Class bodyType);
Mono>> toEntityList(Class element
}
}

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public interface WebClient {
UriSpec> get();
//omitted...
static WebClient create() {
return new DefaultWebClientBuilder().build();
}
interface RequestHeadersSpec> {
//omitted...
Mono exchange();
//omitted...
}
interface ResponseSpec {
Mono bodyToMono(Class bodyType);
Flux bodyToFlux(Class elementType);
Mono> toEntity(Class bodyType);
Mono>> toEntityList(Class element
}
}

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Code Session

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@Autowired
public GitterService(
GitterClient gitterClient
) {
gitterMessageSource = Flux.from(
gitterClient
.getMessages(null)
)
.onBackpressureBuffer()
.publish(1)
.autoConnect(0);
}

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@Autowired
) {
gitterClient
.getMessages(null)
)
.publish(1)
.autoConnect(0);
}
.onBP()

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@Autowired
) {
gitterClient
.getMessages(null)
)
.publish(1)
.autoConnect(0);
}
.onBP()

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.onBP()
@Autowired
) {
gitterClient
.getMessages(null)
)
.publish(1)
.autoConnect(0);
}

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.onBP()
@Autowired
) {
gitterClient
.getMessages(null)
)
.publish(1)
.autoConnect(0);
}

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.onBP()
@Autowired
) {
gitterClient
.getMessages(null)
)
.publish(1)
.autoConnect(0);
}

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.onBP()
@Autowired
) {
gitterClient
.getMessages(null)
)
.publish(1)
.autoConnect(0);
}
…subscribe();

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.onBP()
@Autowired
) {
gitterClient
.getMessages(null)
)
.publish(1)
.autoConnect(0);
}
…subscribe();
…subscribe();

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Message Service

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Code Session

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@Override
public Flux latest() {
return chatClient.stream()
.transform(MessageMapper
::toViewModelUnits
);
}
@Override
::toViewModelUnits
);
}
@Override
::toViewModelUnits
);
}
.transform()

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Statistics Service

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Code Session

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@Autowired
public DefaultMessageService(
MessageRepository messageRepository,
ChatService chatClient,
MessageBroker messageBroker
) {
this.chatClient = chatClient;
Flux saved = messageRepository
.saveAll(chatClient.stream()
.transform(MessageMapper::toDomainUnits)
);
messageBroker.createChannel(
"statisticChanged",
saved.materialize()
);
}

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@Autowired
) {
);
"statisticChanged",
saved.materialize()
);
}
.transform()

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@Autowired
) {
);
"statisticChanged",
saved.materialize()
);
}
.transform()

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@Autowired
) {
);
"statisticChanged",
saved.materialize()
);
}
Channel
.materialize()

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@Autowired
) {
);
"statisticChanged",
saved.materialize()
);
}
.transform()

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@Autowired
) {
);
"statisticChanged",
saved.materialize()
);
}
.transform()

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@Autowired
) {
);
"statisticChanged",
saved.materialize()
);
}
.transform()

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@Autowired
) {
);
"statisticChanged",
saved.materialize()
);
}
.transform()

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@Autowired
) {
);
"statisticChanged",
saved.materialize()
);
}
.materialize()
.transform()

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@Autowired
) {
);
"statisticChanged",
saved.materialize()
);
}
.transform()
.materialize()

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@Autowired
) {
);
"statisticChanged",
saved.materialize()
);
}
Channel
.materialize()

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Channel
@Autowired
) {
);
"statisticChanged",
saved.materialize()
);
}
.materialize()

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@Autowired
) {
);
"statisticChanged",
saved.materialize()
);
}
.materialize()
Channel

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Code Session

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this.statisticPublisher = messageBroker
.channel("statisticChanged")
.retry(err -> err instanceof USE)
.dematerialize()
.flatMap(s -> doGetUserStatistic())
.mergeWith(Mono
.defer(this::doGetUserStatistic)
)
.cache(1);
.retry()
Channel

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